1. Field of the Invention
The present invention relates to a powder slurry coating composition and specifically to a powder slurry coating composition that is excellent in dispersibility of resin in water and can provide a cured film with excellent strength after baking.
2. Description of the Related Art
Powder slurry coatings to be applied are in the form of a dispersion of fine resin particles in water. In such coatings, various additives such as surfactants, thickeners and the like are used to prevent the fine resin particles from gathering or precipitating and to have them stably dispersed in the water (for example, see Japanese Patent Laid-Open No. 2001-220544 and Japanese Patent Laid-Open No. 7-196953 (1995), pp. 3–4.)
In such powder slurry coatings, the base component and the curing agent should be prevented from reacting with each other during the storage. Therefore, the functional group of the curing agent is blocked for use (for example, see Japanese Patent Laid-Open No. 7-196953 (1995), pp. 3–4.)
When the powder slurry coatings with surfactants are practically used, however, the surfactants remaining after the evaporation of the water medium to dryness can worsen the water resistance of the film. The surfactants can also develop a plasticizing effect to worsen the strength of the film.
In addition, the powder slurry coatings with the curing agent having a blocked functional group need a high baking temperature in practical use, because the blocking agent generally needs a very high temperature of 160° C. or higher to entirely react after dissociation. Such a high baking temperature can reduce the productivity because of more time for heating or cooling after the curing and also can cause discoloration of the film after baking. The heat source required for such a high temperature is also undesirable in terms of environment.
If the film formed by applying and baking the slurry coating is exposed to the outdoor environment, it needs acid rain resistance. However, the additives such as surfactants and thickeners remaining in the film formed from the conventional slurry coatings can coagulate as the acid rain vaporizes and therefore worsen the appearance and quality of the film.